1. Field of the Invention
This invention relates to an optical scanning apparatus and an image forming apparatus using the same, and is particularly suitable for a laser beam printer, a digital copier, a multifunction printer or the like having, for example, the electrophotographic process designed such that a light beam emitted from light source means is deflected by deflecting means, and a surface to be scanned is optically scanned through scanning optical means to thereby record image information.
2. Related Background Art
In the optical scanning apparatus of a laser beam printer, a digital copier or the like, a beam optically modulated and emitted from light source means in conformity with an image signal is periodically deflected by deflecting means comprising, for example, a polygon mirror, and is condensed into a spot-like shape on the surface of a photosensitive recording medium by scanning optical means having an fxcex8 characteristic, and is optically scanned to thereby record image information.
FIG. 9 of the accompanying drawings is a schematic view of the essential portions of a conventional optical scanning apparatus. In FIG. 9, a divergent beam emitted from a light source unit 91 is converted into a substantially parallel beam by a collimator lens (not shown), and has its width limited by an aperture (not shown) and enters a cylindrical lens 92 having predetermined power only in a sub-scanning direction. The substantially parallel beam having entered the cylindrical lens 92, in a main scanning cross-section, emerges while keeping the state of the substantially parallel beam. Also, in a sub-scanning cross-section, it converges and is imaged as a substantially linear image on the deflecting surface (reflecting surface) 93a of a light deflector 93 comprising a polygon mirror. The beam reflected and deflected by the deflecting surface 93a of the light deflector 93 is directed to the surface 97 of a photosensitive drum as a surface to be scanned through scanning optical means (an fxcex8 lens system) having first and second scanning lenses (fxcex8 lenses) 95a and 95b having the fxcex8 characteristic, and scans on the surface 97 of a photosensitive drum at a substantially constant speed by the light deflector 93 being rotated at a substantially equal angular speed by a polygon motor 94, to thereby effect the recording of image information.
The first and second scanning lenses 95a and 95b in FIG. 9 are strictly positioned relative to the optical path of the beam deflected by the light deflector 93, and thereafter are fixed to an optical box (housing), not shown, by a known method such as adhesive securing or spring hold-down.
The first and second scanning lenses 95a and 95b are generally inexpensive plastic lenses, and positioning reference surfaces 99a1, 99a2, 99b11, 99b12, 99b21 and 99b22 for positioning in the direction of an optical axis are provided on configurational portions 90a1, 90a2, 90b1 and 90b2, respectively, outside the effective lens areas thereof. That is, on the first scanning lens 95a, the positioning reference surfaces 99a1 and 99a2 are provided on the same plane as the configurational portions 90a1 and 90a2, respectively, and on the second scanning lens 95b, the two positioning reference surfaces 99b11, 99b12 and 99b21, 99b22 are protrudedly provided separately in the sub-scanning direction from the configurational portions 90b1 and 90b2, respectively.
These positioning reference surfaces 99a1, 99a2, 99b11, 99b12, 99b21 and 99b22 are brought into contact with the positioning pins of the optical box, not shown to thereby effect the positioning in the direction of the optical axis, whereby the deterioration of the curvature of image field on the surface 97 to be scanned and the deterioration of the uniformity of the scanning speed (fxcex8 characteristic) is prevented.
Japanese Patent Application Laid-Open No. 09-329755 discloses an optical scanning apparatus in which a scanning lens is provided with a pair of positioning reference surfaces differing in height by a predetermined amount and these are brought into contact with the positioning portion of an optical box, whereby an optical box of the same specification can be applied over a wide range.
Incidentally, recently, with the demand for the compactness of the entire apparatus, the compactness of a scanning optical system as scanning optical means has been contrived and for example, as a method therefor, mention may be made of making the angle of field of the scanning optical system wider or disposing the scanning optical system near a light deflector.
On the other hand, when in an optical scanning apparatus of this type, a beam emitted from a light source is made to be incident on the deflecting surface of a light deflector from a oblique direction thereto in the main scanning cross-section, the position of the beam reflected and deflected by the deflecting surface becomes asymmetrical with respect to the optical axis of the scanning optical system. This asymmetry becomes greater as the angle of field becomes wider, and recently the effective diameter of a scanning lens constituting the scanning optical system and the shape thereof in the main scanning cross-section have also become great in the asymmetry thereof. Along therewith, the configurational portion outside the effective lens area of the scanning lens also becomes great in asymmetry and for example, in FIG. 9, to make a straight line linking the points on two positioning reference surfaces together or a plane formed by the points on three or more positioning reference surfaces orthogonal to the optical axis of the scanning optical system, the amount of protrusion (height) of at least one positioning reference surface must be made great.
The scanning lens, however, is generally a plastic lens, as described above, and when the amount of protrusion becomes great, there arises the problem that the moldability of the lens is aggravated and desired surface accuracy is not obtained.
Also, near the light deflector, there are disposed many members such as a driving motor, a motor substrate, not shown, and a cylindrical lens, and when the scanning lens is disposed near the light deflector, there also arises the problem that a positioning member on the optical box side cannot be disposed due to the physical interference with other member.
It is a first object of the present invention to provide an optical scanning apparatus in which a scanning lens can be positioned highly accurately without aggravating the surface accuracy of the positioning reference surface of the scanning lens, and an image forming apparatus using the same.
It is a second object of the present invention to provide an optical scanning apparatus in which a positioning reference surface is freely disposed such as contriving energy saving, whereby the degree of freedom of the disposition of a scanning lens can be enhanced, and an image forming apparatus using the same.
In one aspect of the invention, an optical scanning apparatus comprises deflecting means for deflecting a beam emitted from light source means, and scanning optical means having at least one scanning lens for causing the beam deflected by the deflecting means to be imaged on a surface to be scanned, wherein the at least one scanning lens constituting the scanning optical means has a plurality of positioning reference surfaces for effecting the positioning of the scanning lens in the direction of the optical axis thereof, and is disposed so that a straight line linking the points on two positioning reference surfaces together or a plane formed by the points on three or more positioning reference surfaces may be non-orthogonal to the optical axis, and in a main scanning cross-section, the shape of the effective portion of the scanning lens is asymmetrical with respect to the optical axis.
In further aspect of the forgoing optical scanning apparatus, the scanning lens of which the shape of the effective portion in the main scanning cross-section is asymmetrical with respect to the optical axis is such that the effective length thereof in the main scanning cross-section differs relative to the optical axis.
In further aspect of the forgoing optical scanning apparatus, the scanning lens of which the shape of the effective portion in the main scanning cross-section is asymmetrical with respect to the optical axis is such that the meridional shape thereof is asymmetrical with respect to the optical axis.
In further aspect of the forgoing optical scanning apparatus, the scanning lens of which the shape of the effective portion in the main scanning cross-section is asymmetrical with respect to the optical axis is such that the effective length thereof in the main scanning cross-section differs relative to the optical axis and the meridional shape thereof is asymmetrical with respect to the optical axis.
In further aspect of the forgoing optical scanning apparatus, there are a plurality of scanning lenses each of which the shape of the effective portion in the main scanning cross-section is asymmetrical with respect to the optical axis.
In further aspect of the forgoing optical scanning apparatus, the plurality of positioning reference surfaces disposed on the at least one scanning lens are provided such that the optical axis is interposed therebetween.
In further aspect of the forgoing optical scanning apparatus, the plurality of positioning reference surfaces disposed on the at least one scanning lens are provided on the end portions of the scanning lens with the optical axis interposed therebetween, and two or more of the positioning reference surfaces provided on the end portions of the scanning lens are provided separately from each other in a sub-scanning direction.
In further aspect of the forgoing optical scanning apparatus, the plurality of positioning reference surfaces are provided protrudingly from a configurational portion outside the effective lens portion of the scanning lens, and the amounts of protrusion of the plurality of positioning reference surfaces from the configuration portion are substantially equal to one another.
In further aspect of the forgoing optical scanning apparatus, the protruding positioning reference surfaces are cylindrically shaped.
In further aspect of the forgoing optical scanning apparatus, the ridgelines between the protruding positioning reference surfaces and the side surfaces of the protruding positioning reference surfaces are formed with a taper.
In further aspect of the forgoing optical scanning apparatus, the plurality of positioning reference surfaces are provided on a configurational portion outside the effective lens area of the scanning lens and are formed on the same plane as the configurational portion.
In further aspect of the forgoing optical scanning apparatus, the positioning reference surfaces are orthogonal to the optical axis.
In further aspect of the forgoing optical scanning apparatus, the scanning lens of which the shape of the effective portion in the main scanning cross-section is asymmetrical with respect to the optical axis is molded out of a plastic material.
In another aspect of the invention, an optical scanning apparatus comprises deflecting means for deflecting a beam emitted from light source means, and scanning optical means having at least one scanning lens for causing the beam deflected by the deflecting means to be imaged on a surface to be scanned, wherein the at least one scanning lens constituting the scanning optical means has a hollow portion in at least one of configurational portions outside an effective lens portion of the scanning lens with the optical axis thereof interposed therebetween, and a positioning reference surface for effecting the positioning of the scanning lens in the direction of the optical axis is formed on the hollow portion.
In further aspect of the forgoing optical scanning apparatus, the scanning lens does not have a hollow portion in the other configurational portion outside the effective lens portion with the optical axis interposed therebetween, and has a positioning reference surface on the other configurational portion outside the effective lens portion, and the positioning reference surface is formed on the same plane as the configurational portion.
In further aspect of the forgoing optical scanning apparatus, the scanning lens has a concave surface, and the positioning reference surface is formed on the concave surface side of the scanning lens.
In further aspect of the forgoing optical scanning apparatus, the positioning reference surface is formed on a surface opposite to an ejector pin.
In further aspect of the forgoing optical scanning apparatus, the scanning lens is molded out of a plastic material.
In another aspect of the invention, an image forming apparatus comprises the foregoing optical scanning apparatus, a photosensitive member disposed on the surface to be scanned, a developing device for developing an electrostatic latent image formed on the photosensitive member by the beam scanned by the optical scanning apparatus as a toner image, a transferring device for transferring the developed toner image to a transferring material and a fixing device for fixing the transferred toner image on the transferring material.
In another aspect of the invention, an image forming apparatus comprises the foregoing optical scanning apparatus and a printer controller for converting code data inputted from an external device into an image signal and inputting it to the optical scanning apparatus.